Sr-ferrite Powder Research Articles

Evaluation of Static Magnetic Fields Produced by Magnetic Floors Composed of Strontium Ferrite Powder Utilized in the Construction Industry

This paper presents a magnetic safety evaluation of the static magnetic field produced by magnetic floors with permanent magnet properties utilized in the construction industry. The magnetic floors analyzed in this paper are composed by a concentration of 85% of isotropic strontium (Sr) ferrite powder mixed with chlorinated polyethylene. The magnetic floors are magnetized and tested in the laboratory to measure the magnetic field levels in different regions of the magnetic floors and magnetic subfloors. Finite-element (FE) simulations are carried out to compute the magnetic field produced by magnetic floors. The numerical results and laboratory tests are compared and analyzed. Values of the magnetic field between 2 and 50 mT are computed and measured in different regions of magnetic floors. Finally, the static magnetic field levels obtained in the magnetic floors are compared with the permitted magnetic field values for different electronic devices, pacemakers, and other common objects utilized by persons in buildings. The results obtained in this paper show that magnetic floors are safe, and they can be employed in buildings without putting in risk electronic devices or persons with pacemakers.

Structural and magnetic properties of Ce3+-substituted Sr-ferrites synthesized by low-temperature calcination ceramic method

Ce3+-substituted Sr-ferrite powder was synthesized through low-temperature calcination ceramic method. The influence of Ce3+ substitution on the microstructure and magnetic properties of Sr-ferrite powder was discussed. Results showed that the Ce3+ ions could completely enter the ferrite lattice when the substitution amount was in the range of x = 0–0.2. The saturation magnetization and intrinsic coercivity of Sr1−xCexFe12O19 ferrites could be enhanced through Ce3+ substitution. These enhancements were attributed to the improvements in the magnetic structure and microstructure.

3D gel-printing of Sr ferrite parts

3D gel-printing (3DGP) opens new possibilities to process complex-shaped Sr ferrite parts for magnetic applications. In this study, a novel 3DGP process based on the hydroxyethyl methacrylate gelation system was employed to prepare complex-shaped Sr ferrite samples. To obtain highly loaded pseudo-plastic slurries, the Sr ferrite powder was modified by 1 wt% silane coupling agent and 2.5 vol% polymer Silok7050S was introduced into the ceramic slurry as a dispersant. In the printed samples, good dimensional accuracy and surface quality were achieved with a relatively low surface roughness of 5 µm. After sintering, the Sr ferrite ceramics exhibited good surface quality and the surface roughness was 3.2 µm. A homogeneous microstructure was observed. The bending strength for the sintered samples with the relative density of 97% was 83 MPa. In addition, the corresponding coercivity, remanence, and maximum magnetic energy product values were 271.2 kA/m, 0.383 T, and 26.34 kJ/m3, respectively.

表面处理剂对聚吡咯/铁氧体复合材料性能的影响

以溶胶–凝胶法制备M型锶铁氧体，在850℃的煅烧温度，不同保温时间的条件下制得粉末样品，并对制备产物的物相、形貌和磁性能利用XRD、SEM等检测技术进行表征。实验结果证明：在850℃煅烧，2 h煅烧时间所得产物都为较纯的锶铁氧体。通过不同的表面处理剂将制得的钡铁氧体在聚吡咯的乳液中通过乳液聚合的方法合成了聚吡咯/铁氧体复合材料。通过对不同处理剂得到的复合材料的矫顽力、磁化强度和电导率的检测，得到表面处理剂对复合材料性能的影响规律。 The M-type Sr-ferrite powders were prepared by using sol-gel method. Powder samples were prepared at 850˚C and different holding time. The phase, size and magnetic properties of the powder samples were characterized by using XRD, SEM and network analyzer. The result indicates that the products that were prepared at 850˚C and 2 h were pure. The ppy/Sr-ferrite composites were obtained by in-situ polymerization method by different treatment agent. By testing the coercivity, magnetization and conductivity of the composites obtained by different treatment agents, The effect of treatment agent on the ppy/Sr-ferrite composites properties was given a detailed explanation.

Effect of microcrystalline wax on the solvent debinding of the Sr-ferrite ceramics prepared by powder injection molding

Powder injection molding (PIM) opens new possibilities to process complex Sr-ferrite components for magnetic applications. In the present study, new binder system with the addition of microcrystalline wax (MW) was used for the Sr-ferrite powder injection molding. The optimum binder composition was determined based on rheological measurement, mircrostructure observation by SEM, thermal change by DSC and debinding process. The results indicated that MW with 10vol.% addition in the binder system containing high density polyethylene (HDPE), paraffin wax (PW) and stearic acid (SA) decreases the defects of the green parts after solvent debinding because the distribution of the binder system between the Sr-ferrite particles becomes more homogeneous. Using the proper binder system containing MW, the defect-free and dense Sr-ferrite ceramics can be prepared after solvent and thermal debinding and sintering. Based on the experimental results, the effects of MW microcrystalline wax on the solvent debinding of the Sr-ferrite ceramics were detailed discussed.

Microstructure and coercivity of Sr1−x−x′LaxCax′Fe2n−yCoyOα ferrites

M-type strontium hexaferrites with the chemical composition of Sr1−x−x′LaxCax′Fe2n−yCoyOα were prepared by ceramic process. X-ray diffraction, X-ray photoelectron spectrometer, scanning electron microscopy, vibrating sample magnetometer and permanent magnetic measuring system were employed to investigate the influence of La–Ca–Co substitution on the microstructure and intrinsic coercivity of the powder and sintered samples. The results show that both Sr-ferrite powders and sintered samples with Ca–La–Co substitution have high intrinsic coercive forces more than 500 KA/m. The acting mechanism of La–Ca–Co substitution on the high coercivity and microstructure was discussed. La–Co substitution causes not only the increase of the anisotropy, but also the decrease of the grain size, which increases the coercivity greatly. The presence of Ca together with La and Co in the substituted system helps to increase the magneto-crystalline anisotropy field. However, it accelerates the sintering and the grain growth, making the intrinsic coercivity of the sintered magnets decrease.

High Characteristic Sr-Ferrite Magnetic Powders Made by New Direct-Spray Roasting.

We have studied the process of new direct-spray roasting; SrCO3 powders were directly added into the 12FeCl2 x 4H2O solution first, and then α-Fe2O3 powders with the particle size of 210-620 nm was made after spray roasting in the low temperature of 400-700 degrees C. The direct-spray roasting enables us to get the uniform mixing of α-Fe2O3 and SrCO3 powders, and to lower the calcination temperature of Sr-ferrite, compared to that of the conventional dry method. Also, the magnetic properties of the powders made by direct-spray roasting are very higher than that made by the dry method. We suggest that the Sr-ferrite powders by the direct-spray roasting act as useful high-Br magnetic powders for high characteristic resin-bonded magnet.

Investigation of inorganic fillers on properties of 2–2 connectivity cement/polymer based piezoelectric composites

The 2–2 cement/polymer based piezoelectric composites containing inorganic fillers were prepared. The influences of filler content and composite thickness on the composite properties were investigated. The results show that graphite powder shows larger effect on dielectric property of the composites than silicon powder and strontium ferrite (Sr-ferrite) powder, especially when graphite powder is larger than 10wt.%. The Sr-ferrite can improve the thickness electromechanical coupling properties of the composites. When Sr-ferrite powder content is 15wt.%, the composite has a kt value of 68.6% at a 2mm thickness. The electromechanical quality factor (Qm) of the composites shows fluctuation variation between 10 and 60 with increasing the composite thickness, which is far less than that of the pure ceramic. The coupling resonance effects between planar mode and thickness mode of the composites was reduced by decreasing the composite thickness, and the pure thickness mode resonance can be obtained at a small composite thickness.

The structure, morphology and magnetic properties of Sr-ferrite powder prepared by the molten-salt method

Sub-micrometre high-performance Sr-ferrite powder was prepared by a molten-salt method using Na2SO4 as the fluxing agent. In the reaction process, a mixture of superfine powder was pre-sintered at 1150 °C for 3 h and then annealed at 850 °C for 2 h. The as-obtained Sr-ferrite powder is SrFe12O19 with a hexagonal magnetoplumbite structure. We observe that with raising the pre-sintering temperature as well as increasing the annealing temperature and time, there is an enlargement of particle size. We regulated the reaction parameters to optimize the magnetic properties of the Sr-ferrite powder. The structure with the best magnetic properties is quasi-cubic in shape and relatively uniform in size, showing a coercivity of 471.89 kA m−1, a saturation magnetization of 91.51 µWb m kg−1, a remanence ratio of 0.50 and a maximum magnetic energy product of 7.89 kJ m−3. We then studied the effects of particle size, demagnetization factor and magnetocrystalline anisotropy on coercivity. Compared with the conventional ceramic process, the one presented here is more convenient and economical for the production of homogeneous hexagonal ferrite powders of high magnetic performance.

Preparation of Strontium Ferrite Powders by Mechanochemical Process

Sr-ferrite powders were preparated by mechanochemical treatments using SrCO3 and Fe2O3 as raw materials. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM) were employed to evaluated the morphologies, structures and magnetic properties of samples. The results indicated that the starting mixture became amorphous stage after ball-milled for 30h, and single phase SrFe12O19 could be obtained after annealed at 900°C for 2h. And the saturation magnetization was 58.2Am2/kg, and coercivity was 281.2 kA/m at room temperature. In comparison with the traditional firing method , the mechanochemical method benefited achieving the higher coercivity, which indicated that the samples had a better magnetic properties.

Magnetic properties of Sr-ferrites synthesized in molten [formula omitted] flux

The Sr-ferrite powders, SrFe 12 O 19 , were synthesized by the molten salt method using ( NaCl + KCl ) mixture. Particle morphology was homogeneous and hexagonal platelet like. Both particle size and thickness increased as the reaction temperature and time increased. The sintering density of Sr-ferrite magnet prepared with powders by the molten salt method showed the maximum value at the sintering temperature of 1200 ∘ C . The magnetic properties of the Sr-ferrite magnet were investigated with various sintering temperatures. The maximum values of remanent magnetization ( σ r , 45 emu/g) and coercivity field ( H c j , 298 kA/m) occurred at the sintering temperatures of 1150– 1200 ∘ C . The Sr-ferrite magnet by a molten salt method showed higher remanent magnetization and coercivity field than those of the Sr-ferrite magnet prepared with the same starting materials by a conventional ceramic process.

염을 이용한 Sr 페라이트의 분말합성과 그의 자성특성

In this study we prepared the Sr-ferrite powders and magnet by a molten salt method using the (NaCl+KCL) salt mixture. Starting materials of Fe₂O₃ and SrCO₃ were mixed as the molar ratio of 5.70:1, and 0.08 mol% Al₂O₃, 0.10 mol% SiO₂ and 0.12 mol% CaO were added as additives. Sr-ferrite powders synthesized at the reaction temperatures of 800~1200℃ showed the typical M-type hexagonal ferrite phase, and hexagonal plate-like morphology with uniform distribution of 1~3 ㎛ particle size. The bulk density of the sintered Sr-ferrite magnet prepared with powders by the molten salt method showed the maximum density of 4.82 g/㎤ at the sintering temperature of 1200℃. The maxima of remanent flux density (Br, 45 emu/g) and coercive force ( i H c , 3.75 kOe) occurred at the sintering temperatures of 1150℃ and 1200℃.

Magnetic anisotropy of Sr-ferrite powder produced by mechanical alloying

Abstract Sr-ferrites were prepared by mechanical alloying and subsequent annealing, and development of anisotropic nature of the Sr-ferrite powders during post-synthesis milling were investigated. The Sr-ferrites in as-synthesised state exhibited poor anisotropic nature, and this was attributed to the unique microstructure of the particle consisting of randomly oriented ultra-fine grains. Anisotropic nature of the Sr-ferrite was developed and improved by the post-synthesis milling, and this was explained by the disintegration of the crystal aggregates into individual grains.

Magnetic Properties of Sr-ferrite Powder Prepared by Intensive Mechanical Milling Technique

As an alternative promising way of producing high coercivity Sr-ferrite for a permanent magnet application, intensive mechanical milling process was applied to the raw materials of the Sr-ferrite with different composition. Synthesising reactivity for the Sr-ferrite of the mechanically milled raw material containing <TEX>$SrCO_3$</TEX>, <TEX>$La_2O_3$</TEX>, <TEX>$Fe_2O_3$</TEX>, <TEX>$Co_3O_4$</TEX>, and <TEX>$SiO_2$</TEX> was inferior to that of the raw material containing <TEX>$SrCO_3$</TEX> and <TEX>$Fe_2O_3$</TEX>, The Sr-ferrite prepared from mechanically milled raw materials had profoundly improved magnetic properties compared to the Sr-ferrite prepared by conventional method. Beneficial effect of the substituting (<TEX>$La_2O_3$</TEX>, <TEX>$Co_3O_4$</TEX>) and additive (<TEX>$SiO_2$</TEX>) oxides for improving the magnetic properties was not exploited in the Sr-ferrite prepared from the mechanically milled raw material. The Sr-ferrite powder prepared from the mechanically milled raw materials was magnetically isotropic in nature.

Microscale resin-bonded permanent magnets for magnetic micro-electro-mechanical systems applications

A micromachining technique has been developed for the fabrication of microscale resin-bonded permanent magnets. Magnetic paste has been prepared from Sr-ferrite powder and an epoxy resin, filled into lithographically defined molds, and formed into resin-bonded magnets after room temperature curing. Coercivity of 356 kA/m (4480 Oe), retentivity of 33 mT (330 G), and energy density of 2.7 kJ/m3 have been achieved in 65-μm-thick disk arrays with lateral dimensions ranging from 50 to 200 μm. Based on the developed magnet, a magnetic MEMS actuator has been designed, fabricated, and characterized. Actuation current up to ±60 mA operated the actuator up to 70 μm in attractive and repulsive motion. This work can be used for producing thick-film type permanent magnets, which can be scaled from a few tens of micrometers to millimeters on various substrates.

磁界配向成形における適正条件の評価基準

Generally the anisotropic permanent magnet is produced by the magnetic field orientation forming, namely, the compaction of magnetic powders under magnetic field. In the magnetic field orientation forming, there is the close relation in degree of orientation and sintering shrinkage of the compact. The sintering shrinkage is simply obtained from dimensional measurement of green compacts and sintered ones. It is proposed that the saturation value of the sintering shrinkage is made to be evaluation criterion for deciding the strength of applied magnetic field in order to find the optimum condition in the magnetic field orientation forming. Though various factors affect the degree of orientation, it is possible to estimate as those accumulation effect by sintering shrinkage. This evaluation criterion is applicable in case of not only the dry compaction of Sr-ferrite powder under magnetic field but also the forming of the compound mixed with a MIM binder.

Direct use of celestite to prepare presintered SrFe 12O 19 powders

Mineral celestite was directly used to prepare presintered single-phase Sr-ferrite powders for fabrication of sintered permanent magnets. The starting materials were high-purity domestic celestite, modified iron oxide and sodium carbonate. The role of sodium carbonate is firstly to promote the displacement solid-state reaction and secondly to lower the temperature during calcining stage. A vibrating sample magnetometer was used to measure magnetic parameters of the powders. The results were compared with those of the powders prepared by conventional ceramic process. Lower reaction temperature of 1000°C and low-cost celestite show that this process is more economical for production of presintered SrFe 12O 19 powders than the conventional one.

磁性材料 Ｓｒフェライト粉とその成形体の磁気特性に及ぽすメカノフュージョン処理の影響

To investigate effects of shear stress and shear strain on the magnetic properties of Sr-ferrite powder, the powder was milled by a mechanofusion (MF) apparatus, and its magnetic characteristics were studied. Coercive force of the MF-milled powder was decreased with milling time, and it reached the constant value of 140 kA⋅m-1 as milling time was longer than 30 min. Reduction of the coercive force of the milled powder was found to slightly improve degree of powder particle alignment under applied magnetic fields. M-type ferrite phase of the original Sr-ferrite powder remains unchanged after the MF-milling treatment. The mean particle size of the powder was increased by a MF-milling treatment longer than 30 min due to aggregation of the powders. As a result, the optimum MF-milling time was in the range from 15 min to 30 min under the experimental conditions of this study.

Studies concerning the optimization of ceramic magnets anisotrope pressing

Abstract This paper presents some research results concerning the optimization of the wet anisotrope pressing of Ba and Sr ferrite powders. The increasing of the structural anisotropy degree – K – of the permanent ceramic magnets by the addition of some surfactants to the liquid of the pressing slurries is the main purpose of this research. Also, there is an exploration of the optimization effects on the anisotrope pressing forming operation from the point of view of the relationship between the microstructural anisotropy degree – K – and the energy improvement – BHmax – of the manufactured magnets.

磁石・磁性材料の化学 Ｉ Ｓｒフェライト粉末を用いたボンド磁石の磁気特性に及ぼす成形条件の影響

磁石・磁性材料の化学 Ｉ Ｓｒフェライト粉末を用いたボンド磁石の磁気特性に及ぼす成形条件の影響